1. Field of the Invention
The present invention relates to a method for producing polymer particles.
2. Description of the Related Art
Polymer particles are produced by various polymerization methods such as suspension polymerization, emulsion polymerization, and precipitation polymerization. Among these polymerization methods, suspension polymerization is industrially widely used as, for example, a method for producing a polymerized toner because a functional substance such as a coloring material can be easily included in polymer particles.
Recently, the area of study regarding a technique for controlling the molecular weight of polymer particles has been activated. For example, Non-Patent Document 1 (Adam Limer, Alex Heming, Ian Shirley, and David Haddleton, European Polymer Journal, 2005, Vol. 41, pp. 805-816) and Non-Patent Document 2 (John D. Biasutti, Thomas P. Davis, Frank P. Lucien, and Johan P. A. Heuts, Journal of Polymer Science: Part A: Polymer Chemistry, 2005, Vol. 43, pp. 2001-2012) describe a method in which living radical polymerization such as atom transfer radical polymerization or reversible addition-fragmentation chain transfer polymerization is combined with suspension polymerization.
However, from the standpoint of problems of, for example, a remaining catalyst, safety and sanitation, and the cost, at present, it is difficult to industrially use many of such living radical polymerization methods.
As a method for industrially controlling the molecular weight of polymer particles, Patent Document 1 (Japanese Patent Laid-Open No. 09-043909) and Patent Document 2 (Japanese Patent Laid-Open No. 2006-221203) describe a method in which a polymerization control agent such as a chain transfer agent or a polymerization inhibitor is used. However, a significant difference in the molecular weight may be caused or the polymerization conversion rate may be significantly decreased depending on a slight difference in the amount of polymerization control agent used.
Although the molecular weight can also be controlled by changing the amount of polymerization initiator or the polymerization temperature, such a method has many problems in terms of the cost and safety for the purpose of obtaining polymer particles having a low molecular weight, for example.
As a method capable of easily controlling the molecular weight at a low cost, Non-Patent Document 3 (Patrick Lacroix-Desmazes, Romain Severac, and Bernard Boutevin, Macromolecules, 2005, Vol. 38, pp. 6299-6309) discloses reverse iodine transfer polymerization.
Furthermore, Non-Patent Document 4 (Jeff Tonner, Patrick Lacroix-Desmazes, and Bernard Boutevin, Macromolecules, 2007, Vol. 40, pp. 186-190) discloses that, in a process of producing polymer particles, the process being performed by using suspension polymerization and reverse iodine transfer polymerization in combination, good molecular-weight controllability and a good polymerization conversion rate can be achieved by adding hydrogen peroxide and hydrochloric acid to an aqueous phase.
The inventors of the present invention found that, in the case where reverse iodine transfer polymerization described in Non-Patent Document 3 is combined with suspension polymerization, iodide ions are produced by hydrolysis of iodine molecules, thereby particularly degrading molecular-weight controllability.
In the method disclosed in Non-Patent Document 4, oxygen produced by thermal decomposition of hydrogen peroxide inhibits a polymerization reaction, and therefore, the polymerization conversion rate is fundamentally insufficient. Furthermore, since this method is suspension polymerization under a strongly acidic condition, dispersion stability of polymer particles may be impaired.